JavaScript Object Notation (JSON) is a data-interchange format that is becoming the format of choice for many commercial products and research products. One of the most typical operations performed on sets of JSON documents, and other document formats such as XML and HTML, is the processing of structural queries, which matches data based on structural patterns, besides specific field values. The expressiveness of structural queries makes it difficult to apply the indexing procedure designed for relational data and queries. The lack of a schema associated with JSON documents further impedes the applicability of traditional techniques for speeding-up query processing (e.g., using secondary indexes).